Carbon nanotubes have a structure with excellent strength and elasticity, and are expected to provide improvement in resin strength and elasticity by their addition to resins in trace amounts. However, because carbon nanotubes are insoluble in resins and solvents, it is difficult to achieve their adequate dispersion in resins and solvents.
Research is therefore being focused on introducing functional groups into carbon nanotubes, and thus improving their dispersibility in solvents. For example, an article in Science 280, 1253(1998) reports on the introduction of carboxylic acid groups into carbon nanotubes using nitric acid or sulfuric acid.
The article in Science 282, 95(1998) presents a method of cutting carbon nanotubes by acid treatment for introduction of carboxylic acid, followed by acylhalide conversion of the carboxylic acid with thionyl chloride to obtain an acyl halide which is then reacted with an amine to obtain an amide derivative. However, this method has adverse environmental consequences since it uses a halide such as thionyl chloride for the reaction, while the high reactivity of the obtained acyl halide also renders its unstable, making its isolated production difficult.
An example of attempting to micronize carbon fibers is reported in Science 280, 1253(1998), wherein heat or ultrasonic waves are applied in the presence of, for example, nitric acid or sulfuric acid to cut and micronize single-walled carbon nanotubes. Yet, even though the carbon nanotubes are cut by acid treatment, the carbon nanotubes aggregate during separation treatment such as filtration and therefore it has been necessary to carry out further dispersing treatment for use as a composite with polymers.
An example of coating the surfaces of carbon fibers with a polymer is disclosed in Japanese Unexamined Patent Publication HEI No. 3-287821, wherein the surfaces of fine carbon fibrils are coated with a polyolefin such as polystyrene, polyethylene or polyacrylic acid, to improve the surface wettability.
Also, Japanese Unexamined Patent Publication HEI No. 5-106163 discloses a method of adhering a carbodiimide reagent to carbon fiber surfaces to improve adhesion at the interface with thermoplastic resins such as polyamides and polycarbonates.